John Ruddock was born on May 20, 1897 in Lima, Peru as John Reynolds Ruddock. He was the first of seven children of his British father and American mother. After the family returned to England he was sent to school at Saint Lawrence College, Ramsgate, Kent from 1910 to 1914.
He worked briefly for an insurance company in Liverpool before volunteering to fight in the First World War. He was commissioned into the Royal Northumberland Fusiliers and saw action on the Somme and at Passchendaele. He was wounded several times and on one occasion was buried for fifteen hours as a result of an artillery bombardment.